Exhaust-gas turbocharger

ABSTRACT

An exhaust-gas turbocharger ( 1 ), having a shaft ( 2 ) on which are arranged a compressor wheel ( 3 ) and a turbine wheel ( 4 ), a bearing housing ( 5 ) in which are arranged a compressor-side bearing arrangement ( 6 ) and a turbine-side bearing arrangement ( 7 ) for the shaft ( 2 ), an oil inflow line ( 8 ) and an oil outflow line ( 9 ), and an additional oil accumulator ( 10 ) for the bearing arrangements ( 6, 7 ) of the shaft ( 2 ). The oil accumulator ( 10 ) is a pressure accumulator arranged in a branch line ( 11 ) of the oil inflow line ( 8 ), and a controllable valve ( 13 ) is arranged between the oil accumulator ( 10 ) and the opening-in point ( 12 ) of the branch line ( 11 ) into the oil inflow line ( 8 ).

The invention relates to an exhaust-gas turbocharger according to thepreamble of claim 1.

An exhaust-gas turbocharger of said type is known from EP 2 054 597 B1.

For the supply of lubricant to the bearings of the shaft, saidexhaust-gas turbocharger utilizes the engine oil pump of the internalcombustion engine on which the turbocharger is mounted.

As a result of the lengths of the lines or ducts, the viscosity of thelubricant, manufacturing tolerances and other influences, however, thereis a delay in the build-up of pressure, and therefore a delayed supplyof lubricant to the bearing system of the exhaust-gas turbocharger,during an engine start.

A similar problem can also occur during the stopping of the engine whenthe exhaust-gas turbocharger overruns on account of its mass inertia. Inboth cases, the bearing arrangement runs through the mixed frictionphase, wherein furthermore, during a renewed engine start, the lubricantremaining in the exhaust-gas turbocharger is heated by the residualheat.

This has the result that the viscosity of the lubricant falls and thelubricating properties are degraded yet further.

The described problems can, in extreme applications such as for examplein hybrid applications or a very high number of start/stop cycles, leadto damage to the bearing arrangement of the exhaust-gas turbocharger andtherefore to failure of the overall system.

Therefore, in the generic exhaust-gas turbocharger according to EP 2 054597 B1, an additional oil accumulator is provided which, in saiddocument, is referred to as an emergency oil tank and extends in theaxial direction over all the radial bearings. Since gravitational forceis used to provide an oil supply in said system, the emergency oil tankis arranged above the radial bearings and at a small radial distancefrom said bearings.

Tests carried out within the context of the invention have however shownthat, specifically in the extreme applications mentioned above, anadditional oil supply of said type which is based on gravitational forceis often not sufficient.

It is therefore an object of the present invention to provide anexhaust-gas turbocharger of the type specified in the preamble of claim1, which always permits a sufficient supply of oil to the bearingarrangements of the charger shaft at a standstill and during thestart-up of the exhaust-gas turbocharger.

Said object is achieved by means of the features of claim 1.

The additional oil accumulator of the exhaust-gas turbocharger accordingto the invention is designed as a pressure accumulator. To avoid mixedfriction states during a start/stop cycle of the exhaust-gasturbocharger, lubricant is supplied in a dosed fashion to the bearingarrangement thereof by means of said pressure accumulator.

For this purpose, during engine operation, a partial quantity of thelubricant in circulation is extracted and temporarily stored in thepressure accumulator as pressurized lubricant. For this purpose, use maybe made of a hydraulic accumulator such as is known from the field ofhydraulics.

By means of a controllable valve on the pressure accumulator andpreferably a further simple check valve in the inflow line for thelubricant, it is possible for lubricant to be supplied in a dosedfashion to the bearing arrangements during the starting and stopping ofthe engine.

It is possible here for the check valve in the inflow line to beexchanged for a controllable valve, in particular check valve, or apressure differential valve.

If a pressure differential valve is used, the pressures on both sides ofthe valve are utilized to generate a movement of the valve in order torealize a build-up or dissipation of pressure in the inflow line and/orin the pressure accumulator and during start/stop cycles.

If a controllable valve, in particular check valve, is used, thepressure signals of the inflow line and of the accumulator system areevaluated and linked by means of an actuation strategy in such a waythat a uniform pressure build-up takes place in the bearing system.

Here, it is possible according to the invention for the system to bedesigned as an external or internal system.

As an internal system, it is possible here for the components of thepressure accumulator, of the valves and of a control device to beintegrated in the bearing housing of the exhaust-gas turbocharger.

Further details, advantages and features of the present invention willemerge from the following description of an exemplary embodiment on thebasis of the drawing, in which:

FIG. 1 shows a perspective, cut-away illustration of an exhaust-gasturbocharger showing the basic components not illustrated in FIG. 2, and

FIG. 2 shows a schematically simplified illustration of an exhaust-gasturbocharger according to the invention.

An exhaust-gas turbocharger 1 according to the invention illustrated inFIG. 2 has not only the components illustrated in said figure but alsothe components shown in FIG. 1, specifically a shaft 2, a compressorwheel 3, a turbine wheel 4 and a bearing housing 5. A compressor-sidebearing arrangement 6 and a turbine-side bearing arrangement 7 formounting the shaft 2 are arranged in the bearing housing 5.

The exhaust-gas turbocharger 1 according to the invention self-evidentlyalso has all the other conventional components of modern turbochargers,but these are not of importance for the description of the presentinvention.

According to FIG. 2, the exhaust-gas turbocharger 1 also has an oilinflow line 8 and an oil outflow line 9 which are hydraulicallyconnected to the engine oil circuit of the engine on which theexhaust-gas turbocharger 1 is mounted.

The exhaust-gas turbocharger 1 according to the invention also has anadditional oil accumulator 10 which is designed as a pressureaccumulator and arranged in a branch line 11 of the oil inflow line 8.As shown in FIG. 2, a controllable valve 13 is inserted between the oilaccumulator 10 and the opening-in point 12 of the branch line 11 intothe oil inflow line 8. The controllable valve 13 can be opened andclosed by means of a control device 14, wherein the control device 14for this purpose uses pressure signals from the inflow line and from thepressure accumulator 10, said pressure signals being symbolized in FIG.2 by the dashed line DS.

Also provided in the oil inflow line, upstream of the opening-in point12, is a simple check valve 15 which may also be replaced with acontrollable valve.

By actuating the valves 13 and 15, the pressure accumulator 10 can becharged with pressurized lubricant when sufficient oil pressure has beenbuilt up by the oil pump of the engine.

During start/stop processes, it is then possible, by means of thelubricant temporarily stored in the pressure accumulator 10 and theactuation of the valves 13 and 15, for lubricant to be supplied in atargeted fashion to the bearing arrangements 6 and 7 of the exhaust-gasturbocharger 1 in order to prevent the non-ideal bearing conditionsresulting from insufficient lubrication, as explained in theintroduction.

In addition to the above written disclosure of the invention, referenceis hereby explicitly made to the diagrammatic illustration thereof inFIGS. 1 and 2.

LIST OF REFERENCE SYMBOLS

-   1 Exhaust-gas turbocharger-   2 Shaft-   3 Compressor wheel-   4 Turbine wheel-   5 Bearing housing-   6 Compressor-side bearing arrangement-   7 Turbine-side bearing arrangement-   8 Oil inflow line-   9 Oil outflow line-   10 Oil accumulator/pressure accumulator-   11 Branch line-   12 Opening-in point-   13 Valve-   14 Control device-   15 Check valve-   DS Pressure signal

1. An exhaust-gas turbocharger (1), having a shaft (2) on which arearranged a compressor wheel (3) and a turbine wheel (4), a bearinghousing (5) in which are arranged a compressor-side bearing arrangement(6) and a turbine-side bearing arrangement (7) for the shaft (2), an oilinflow line (8) for supplying oil to the bearing arrangements and an oiloutflow line (9), and an additional oil accumulator (10) for the bearingarrangements (6, 7) of the shaft (2), wherein the oil accumulator (10)is a pressure accumulator arranged in a branch line (11) of the oilinflow line (8), and wherein a controllable valve (13) is arrangedbetween the oil accumulator (10) and an opening-in point (12) of thebranch line (11) into the oil inflow line (8).
 2. The exhaust-gasturbocharger as claimed in claim 1, including a control device (14) foropening and closing the controllable valve (13) as a function ofreceived pressure signals (DS) from the inflow line (8) and the oilaccumulator (10).
 3. The exhaust-gas turbocharger as claimed in claim 1,wherein a check valve (15) is arranged in the oil inflow line (8)upstream of the opening-in point (12) of the branch line (11).
 4. Theexhaust-gas turbocharger as claimed in claim 1, wherein a controllablevalve is arranged in the oil inflow line (8) upstream of the opening-inpoint (12) of the branch line (11).
 5. The exhaust-gas turbocharger asclaimed in claim 1, wherein a pressure differential valve is arranged inthe oil inflow line (8) upstream of the opening-in point (12) of thebranch line (11).
 6. The exhaust-gas turbocharger as claimed in claim 1,wherein the oil accumulator (10) and the valves (13, 15) and also thecontrol device (14) are integrated into the bearing housing (5).
 7. Theexhaust-gas turbocharger as claimed in claim 1, wherein the oilaccumulator (10) and the valves (13, 15) and also the control device(14) are an external system.